[Dbix-class] Re: Reusing defined columns (inheritance?)

[Darren Duncan]

On 1/2/2014, 1:24 AM, Hartmaier Alexander wrote:
> On 2013-12-30 20:51, Dmitry Latin wrote:
>>> That's why frew wrote
>>> https://metacpan.org/pod/DBIx::Class::Helper::Row::SubClass.
>>>
>> Yeah, but it works only with one parent. I want to subclass from 2 parent
>> classes.
>>
>>
> Use roles instead of multiple-inheritance, much easier to get right!

I second that.

Generic columns such as eg creation date that have the same meaning in all the 
tables they appear, eg this record was created then, conceptually this is a role 
relationship not a subclass relationship.

A subclass relationship refers to things about which this statement is true: 
"<subclass> is a <superclass>", whereas your example is more of a "<class> has 
datestamped role.

Of course, conceptually the difference between class and role can blur 
completely if you look at it from the perspective of each being a subtype of a 
generic instantiable type where the definition of each is like "type foo is 
subset of type object where has the columns {id, creation date, ...}" (this is 
distinct from saying "has only the columns" but you can do that too).  And 
unlike some languages, it is trivially easy in Perl to implement types that way, 
the generic instantiable type being a Perl hash say.

-- Darren Duncan